Describing the blood flow structure and identifying the boundaries of physiological blood circulation norm is among the central problems of physiology, clinical pathophysiology, cardiology, and heart surgery.
The early results of studies of the structural blood flow organization were produced by high-speed filming of blood movement that visualized transport of radio-opaque compositions added to the blood stream. It was found that the blood flow had current lines corresponding frequently to a spiral and that the blood streams did not practically intermix in the central parts of the cardiovascular system, namely, the heart and great vessels. It was shown then that a normal blood flow was not turbulent, that it had a thin boundary layer on the walls of the flow channel, and that it was characterized by insignificant energy dissipation downstream.
As direct methods to measure blood velocity in the flow (electromagnetic flow meters, film thermo-anemometers, and Doppler ultrasonic pulse velosymmetry) came into use, it was established that both the insignificant thickness of the boundary layer and the complex profile of longitudinal velocities in the heart and aorta do not unambiguously confirm that the flow is either laminar or turbulent.
In the latter half of the 1970s, morphological studies and physical modeling, along with cine-angiography and ventriculography helped to discover:                asymmetric conjugation of the principal cavities in the main part of the cardiovascular system that helps swirl the stream;        spiral orientation of some of the intracardiac trabeculas;        fragmentary visualization of blood flow swirling in the central circulation parts; and        spiral orientation of the nuclei of endothelial cells in the aorta corresponding to the direction in which shear stresses are applied.        
These findings led to an assumption that the blood in the central parts of the circulation system flows in the form of a swirled stream, and yet direct visualization and determination of the structure of a real or modeled flow were unsuccessful.
Development of new methods to study fluid flows (MP-tomography and MP-velosymmetry, color Doppler-echocardiography, and laser anemometry) offered opportunities for three-dimensional measurement of the velocities in the blood flow. For example, color Doppler-echocardiography showed swirling in the blood flow in the aorta, and MP-velosymmetry registered episodes of an axisymmetric swirled blood flow in the heart and several major arteries. These studies, too, failed to provide a quantified description of the blood flow because of the absence of analytical or numerical methods for modeling current in a channel of complex geometric configuration such as a blood stream.
Still, a number of products were offered for heart surgery on the basis of empirical observations suggesting flow swirling to improve their functional characteristics.
In the absence of an adequate hydrodynamic model of swirled flow, designers of these products could not use quantified ratios associating blood flow characteristics with the geometry of the flow channel of the streams formed. Besides, these assumptions disregarded the structural specifics and the non-stationary nature of the swirled blood flow.
As a result, the flow modeled on the basis of these assumptions could not restore the normal hydrodynamic characteristics of the blood circulation system without producing stagnation zones and flow separation zones that are factors provoking thrombosis, blood injury, and hyperplasia in the blood stream.
The proposals described below as prior art could not, therefore, be used as functionally complete organ-substituting devices for the cardiovascular system.
In particular, a method currently known to be used to form a blood flow at the cannula outlet was chosen as immediate prior art (Patent RU 2233632 C1, Aug. 10, 2004). The desired effect is achieved, in the view of the inventors of the prior art device, by forming a rotationally translational blood flow in a curved serpentine channel so that the flow actively interacts with the curved walls of the channel and receives a swirl. According to the inventors, blood flow swirling by their method is maintained over a length of the downstream rectilinear portion.
The prior art method, however, does not create conditions in which a flow swirled around the axis of a curved channel develops and maintains rotation around its own axis of symmetry. The method disregards the considerable losses of flow energy as the flow interacts with the wall, nor does it have the conditions to prevent formation of stagnation zones. All parameters of flow swirling are of a speculative, qualitative nature, and are not supported experimentally.
Apart from the above, the prior art method has the following drawbacks:                absence of conditions for the parameters of the swirled blood flow and cannula design (radius, curvature and pitch of flow swirling, and so on) to conform to the patient's individual blood circulation norms;        absence of desired boundary conditions of the swirled flow in the cannula to define conditions for interaction between the blood flow and the walls of the flow channel;        absence of desired initial conditions needed to form a swirled flow in the coil, which conditions determine the velocity field in the flow, its space and time characteristics, the shape of the flow channel, and direction of flow;        disregard for the non-stationary nature of the flow such as changes in the flow velocity components over the cardiac cycle; and        restriction of the possible types of cannulas to a single design of the prior art invention.        
The cannula of the immediate prior art invention allows, in the inventors' view, a right- or left-hand swirl to be given to blood flowing through a spiral-shaped coil. This invention cannot be exercised because the flow takes a direction corresponding to the spatial orientation of the coil walls and cannot be swirled around its own axis, for which reason it is not a swirled flow.
A prior art vessel prosthesis comprises a tube provided on the inside surface with a relief to swirl the blood flow (Patent RU 2153360 C2, Feb. 27, 1995). This prior art prosthesis is disadvantageous because it cannot produce a blood flow having desired characteristics corresponding to the patient's individual norms.
A prior art heart valve prosthesis comprises elements to direct the blood flow, said elements possibly having an axial symmetry and curved cusps and/or body so that a swirled flow is formed as blood flows around them (WO 02/062271).
The prior art device is disadvantageous because it does not provide conditions for joining the flow upstream of the valve, at the valve, and downstream of the valve. This inconsistency leads to further energy losses and flow disturbance at the valve, increasing the risk of thrombosis and blood injury and lowering the functional characteristics of the device.
A prior art pump for an assist blood circulation system that forms a swirled blood flow comprises a chamber having valves arranged opposite one another and a guide in the form of an Archimedean spiral (GB 2,371,230, Jul. 24, 2002).
This device is disadvantageous because it lacks conditions for joining currents upstream and downstream of the pump, for which reason it cannot prevent formation of stagnation zones and flow separation zones and, therefore, it increases the risk of thrombosis and blood injury in the through-flow chamber of the pump.
A prior art swirling device in the form of a nozzle has guide elements on the inside surface thereof (Patent SU 699125 A, Nov. 30, 1979). This device is disadvantageous because it cannot be used to form a flow of blood or model fluid having desired swirling characteristics.